(1) Field of the Invention
This invention relates to a novel method of producing graphite-containing copper alloys, and more particularly to a method of producing copper alloys in which graphite particles are uniformly dispersed.
(2) Description of the Invention
Generally, alloys containing a solid lubricant are used for the mechanical slide contact parts in internal combustion engines, lubricant containing alloys were deduced from the necessity of complementing the lubricating performance by the own lubricating action of the solid lubricant in case the lubricating oil film is broken. It is well known that graphite can be widely used as such solid lubricant, and there have been produced various kinds of alloys containing graphite.
However, there still remain some difficult problems to be solved. For instance, when graphite is added to an even relatively light material such as aluminum, graphite might float-up and can hardly be dispersed uniformly, and it is to be particularly noted that no graphite and copper alloy of any practical value is so far available. This is ascribable, for one thing, to the following reason: graphite and copper are scarcely soluble to each other and also they differ largely in specific gravity, so that even if the graphite particles are charged into and dispersed in a molten bath of copper or copper alloy, they would float-up to cause unbalanced dispersion when the melt it cast into a mold. Such propensity is intensified proportionally to the size of the ingot produced.
As a novel technique for dispersing graphite, without causing float-up thereof, into a metal which is scarcely soluble with graphite (solubility in graphite being less than 0.005%), that is, a metal which is metallurgically termed as having no compatibility with graphite, there has been proposed recenty a method in which the graphite particles clad with metal coating such as nickel or copper coating are suspended in a gaseous dispersant and blown into the molten bath of a metal having no compatibility with graphite. This method has provided satisfactory results in applications to the metals having no compatibility with graphite, such as aluminum, zinc, magnesium and the like, but it still could not produce a satisfactory result in application to copper. There has been thus no alternative but relying on the powder metallurgical techniques for combination of copper and graphite. However, employment of such power metallurgical techniques requires higher expenditure than needed in casting, and also the obtained sintered products would prove to be inferior in mechanical properties to the castings or cast-forgings. Thus, a strong request has been voiced in the industry for development of a novel casting technique allowing uniform dispersion of graphite in copper without causing float-up of graphite.